The invention is in the field of x-ray imaging and particularly relates to body section radiography, and more particularly relates to methods and systems for generating x-ray images using digital processing of raw image data.
It is well known that body section radiography techniques produce x-ray images of body parts. In early forms of x-ray imaging, x-rays were directed through the body part of interest to an x-ray detector, which provided an image based on the intensity distribution of the x-ray incident on the detector. Images produced by such techniques suffered from structured or anatomical noise which often obscured a lesion or abnormality. Structured noise is caused by normal tissue overlying or encompassing a lesion, for example. Digital processing techniques have been developed which reduce the effects of structured noise. One such technique is generally known as digital tomosynthesis. That technique utilizes digitized x-ray intensity information obtained from an array of points in a detector medium, such as radiographic film, or a digital detector. From that detected intensity data, signals are generated which are representative of the x-ray absorption of the region-to-be-imaged.
X-ray imaging has become an effective way of detecting early breast cancer. With the increasing prevalence of digital imaging, digital mammography is expected to replace film-screen mammography as the best method for the detection of breast cancer. Digital imaging is also expected to replace film-screen imaging in other areas of radiology. The introduction of digital detectors provides the opportunity to bring several methods to radiological imaging which were previously impractical. Among these methods is improved digital tomosynthesis. In mammography, implementation of this technique may result in increased survival from breast cancer, decreased mortality and a reduction in negative biopsies.
In conventional film-screen tomography methods, an x-ray source and a radiographic film-screen detector move in opposite directions, such that only features substantially in one plane of the image remain in sharp focus. Two such techniques are illustrated schematically in FIGS. 1 and 2. The Twinning technique, illustrated in FIG. 1, involves simultaneous, linear x-ray tube and detector motions, about a fulcrum in the object plane, to produce an image of the object that has only one object plane in sharp focus. The projections of features from all other planes are blurred. Using this technique, there is a range about the object plane that is considered to be "in focus". This range is referred to as the section thickness. In general, section thickness is inversely proportional to the amplitude of motion (in degrees) of the x-ray source.
The Grossman technique, illustrated in FIG. 2, is similar to the Twinning technique but involves a rotational movement of the x-ray tube and detector, again as a unit about a fulacrum point but of a fixed distance from each other. With both of these techniques, one or more exposures are necessary for each tomography plane that is imaged as well as full motion of the x-ray tube and detector through the tomographic angle.
In prior art digital tomosynthesis using the Grossman technique, multiple images are acquired as the x-ray tube is moved in an arc above the object and detector. Prior art tomosynthesis has also been accomplished using the Twinning method. By shifting and adding the images, it is possible to reconstruct any plane in the image from this limited set of images. However, such techniques have only been applied to body section imaging with detectors and sources that move with respect to the object being imaged. As a consequence, uncertainties in the position of both the source and detector contribute to image blurring.
It is an object of the invention to provide an improved tomosynthesis system and method. Another object is to provide a tomosynthesis system and method requiring low x-ray dosage. Yet another object is to provide a tomosynthesis system and method permitting generation of accurate and high resolution body section images. Still another object of the invention is to provide a tomosynthesis system having reduced mechanical complexity and increased accuracy as compared to the prior art.